This invention relates to recording members containing heat-reactive components and, more particularly, to recording members capable of being used in thermographic copying, thermal printing, event recording, and as transparencies for overhead projection.
Heat sensitive sheets containing the cyclic polyketo compounds of this invention, useful for copying and recording and characterized by an ability to form a mark of contrasting color when heated to an activation temperature of 50.degree. C., are known in the art. They are used in thermographic processes wherein a recording member is positioned on a graphic original and exposed to infrared radiation to cause selective heating of the dark areas of the original sufficient to form a copy thereof on the heat sensitive member. The thermally responsive members have also been used to record the heated portions of a thermal print-head and to record a colored trace when contacted by the hot stylus of a thermal recorder. The ninhydrinamine reaction wherein ninhydrin reacts with amino acids, primary amines, and certain derivatives of morpholine, piperidine, and pyrrolidine to give the dye commonly referred to as Ruhrman's purple is well known. Isatin reacts with these same amines to give isatin blue. Alloxan reacts with the amines to give a red dye. These reactions have been used in numerous inventions for thermally responsive copy and recording papers and films. Lawton, U.S. Pat. No. 3,736,166 used ninhydrin with various morpholine and piperidine derivatives to prepare transparencies for overhead projection. Lawton, U.S. Pat. No. 3,293,061 combined ninhydrin or hydrindantin with isatin-amine condensates to provide thermographic copy sheets. Bauman and Lawton reacted ninhydrin or hydrindantin with complexes of amines and flavans or phenolic compounds to make thermographic copy sheets, see U.S. Pat. No. 3,149,991 and U.S. Pat. No. 3,149,992. Huffman, U.S. Pat. No. 3,664,858 combined ninhydrin with the adducts of morpholine or piperidine and organic acids in thermal recording members. Sus, U.S. Pat. No. 3,024,362 combined hydrindantin with amino acids or salts of primary amines with organic carboxylic and sulfonic acids to make a thermocopy paper. Allen, U.S. Pat. No. 2,967,785 used the adducts of morpholine or piperidine with isatin or ninhydrin as the color forming material in thermocopy papers. Small, U.S. Pat. No. 3,573,958 combined an amine with a halide or organometallic halide of germanium, silicone, lead, and tin with hydrindantin to provide a heat sensitive recording sheet. In each case the normal dye formations of Ruhrman's purple with ninhydrin, red dye with alloxan, and isatin blue were obtained.
It is often desirable and an objective of this invention to obtain colored records which have colors differing from those normally obtained with the above cyclic polyketo compounds.
Undesirable odors and fumes are obtained by the heat dissociation or decomposition of the complexes, salts, or adducts during the imaging process. There is a problem of image bleaching during excessive heating, on aging, or prolonged exposure to ultraviolet containing light.
Other types of heat sensitive recording sheets are also well known in the art. This invention is related to the use of a leuco or colorless form of a dye material and a phenolic material which reacts with the leuco material to form a colored dye. There are many systems of this type represented in the patent literature.
References for these systems include: